Scroll wheel test

Inspect the WheelEvent stream your browser receives: vertical and horizontal direction, raw units, comparable estimates, delivery timing, reversals, and large variations.

No permission requests · no data leaves this page

How to use

Select Start capture. The bounded test surface receives focus and holds page scrolling only while capture is active and your pointer is inside it.

Scroll slowly in one direction, pause, then reverse. Try horizontal tilt, a side wheel, Shift-scroll, or a trackpad gesture if supported.

Review raw deltas, units, gaps, and marked variations. Stop capture to restore normal scrolling over the surface; Reset all starts a clean run.

Ready. Start capture when your pointer is over the test surface.

Wheel capture surface

Inactive · normal page scroll

Start capture, then scroll here When inactive, wheel gestures over this surface behave normally and move the page.

Raw delta X —

Raw delta Y —

Raw delta Z —

Waiting for a trusted WheelEvent. Raw values and their original unit stay visible.

Active capture calls preventDefault only for cancelable wheel events inside this surface. Page scrolling elsewhere remains available. Ctrl-wheel zoom and middle-button autoscroll are also held inside the active surface.

Delivery summary

Trusted wheel events 0 0 with movement

Delivery rate 0/s peak 0/s · browser delivery

Latest event gap — 0 new-burst gaps ≥600 ms

Direction reversals 0 same axis within 600 ms

Zero-delta events 0 kept, but excluded from patterns

Synthetic ignored 0 isTrusted was false

Reported deltaMode counts

Pixel 0
Line 0
Page 0
Other 0

Vertical axis

Y activity

−Y up 0 · +Y down 0 Reversals 0 · large variations 0 No comparable non-zero samples yet.

Horizontal axis

X activity

−X left 0 · +X right 0 Reversals 0 · large variations 0 No comparable non-zero samples yet.

Comparable stream

Step consistency

Collecting samples Needs 6 values on the same axis and in the same raw unit. Mixed-axis events 0 · modified events 0

Optional wheel switch

Middle-button press

Untested Down 0 · Up 0 · completed 0 Press and release the wheel inside the active surface. This checks only browser button 1, not scrolling.

Data boundary

What “normalized” means

Pixel mode is retained as reported. Line mode is multiplied by the surface’s computed line height; page mode by its current height. Both conversions are labeled estimates, never physical distance.

Interpretation boundary

Markers are not diagnoses

A large variation is over 3× a rolling median after 5 comparable values. Acceleration, coalescing, momentum, drivers, and deliberate speed changes can all create it.

Recent trusted WheelEvents

Newest first · 0/50 entries

No trusted wheel events captured yet.

Direction is browser intent

Positive X and Y normally mean toward the page’s right and bottom. Natural scrolling, Shift-scroll, remapping, zoom gestures, and drivers can change the relationship to your physical motion.

A browser cannot identify the source

WheelEvent can come from a notched wheel, free-spin wheel, side wheel, trackpad, mouse ball, or another equivalent input. This page does not claim which device produced it.

Rate is event delivery, not polling

Browsers and operating systems may combine, accelerate, delay, or throttle events. Events per second and gaps describe this page’s delivered stream, not hardware polling rate or wheel notches.

Compare before concluding

Repeat a slow one-direction run, then compare another browser, port, device, and driver setting. Rapid reversals or large deltas can be clues, but this test alone cannot prove a hardware fault.